The present invention relates to a process for producing shaped parts from synthetic and similar workable materials and a device for the production of shaped parts.
With the present state of development of process technology for formed articles from elastomers and similar workable materials, there are, in principle, two ways of increasing economy of operation. One is the chemical-thermic way, applying the Vant't Hoff Rule, according to which the reaction speed of interlacing doubles with every 10.degree. of temperature increase. The second is another manufacturing process which seeks to optimize all other process parameters. The sum of these two approaches results, among others, in multi-station installations fed by spraying machines, which method is the most economical method so far, but only for the large-quantity production of formed articles. ("Gummi-Asbest-Kunststoffe," 1971, pp. 460 - 466 and 468).
Depending on the tool design and the feeding of blanks, three processes can be distinguished in the manufacture of formed articles:
A. THE COMPRESSION PROCESS
B. THE TRANSFER PROCESS
C. THE INJECTION PROCESS.
Articles where rework to remove lateral waste (flash) is expensive are to advantage produced by methods b or c.
At the present time, the most popular machine for the production of formed articles is the single press of vertical or horizontal design with single or multiple stories (levels). It comprises a mounting table for the rigidly installed forming tools which are replaced after the desired production quantity is reached. The mounting table limits the number (corresponding to the article dimensions) of engravings or "nests" which are located in the form separation plane.
Every single press, also referred in the technical literature as forms carrier, is to be considered as an independent aggregate, since on it all machine parameters such as lifting, lowering, pressure, temperature and time can be set individually. The advantage of such a type of manufacturing is the simple adaptation to the multiplicity of products manufactured; its disadvantage is the exclusive single usage of identical or similar machine and control elements of which several are available. With the round-table principle to accommodate several of the above-mentioned single presses, there was recently created a manufacturing method which offers considerable economical advantages in the manufacture of large quantities.
The forms are filled by an injection aggregate and travel step-by-step during the heating or cooling interval to the mold release station. This means that, aside from the desired production figures, the necessary heating time of a specific product determines the selection of the most economical number of presses on the round table. Furthermore, the large mass of several single presses to be moved limits at the present time the size of the round table to a maximum of 10 form carriers with a total weight of over 100 metric tons.
Also with the round-table installations, the advantage of low article production cost entails the disadvantage of high capital investment and, above all, poorer flexibility. The injection unit of a multi-station installation can simultaneously process only one material, while as a rule a production enterprise uses a large number of different mixtures at the same time.
The two described processes for the manufacture of formed articles, of small- and medium-size production in single presses, and the large-scale production in multi-station installations, have in common one important criterion: For each forming tool in usage, one press must be available as form carrier. In each case, the form carrier must be adjustable individually in order to transmit pressure and temperature to the tool via a given displacement/time program.
If, for instance, in a plant ten articles with small lot sizes must be produced at the same time, they usually require, in addition to the tools, ten similar single-stage presses and ten machine controls operating independent of one another. However, when dealing with large production runs, to be produced on ten round-table installations with ten stations, one requires a total of one hundred forming tools in 100 presses with 10 controls. In both cases, each forming tool, depending on article size and pressing process, contains up to 100 and more form nests which after opening the press at the end of the heating cycle are mostly removed by hand. Equally time consuming is the usually following deburring of the formed article so manufactured.